1. Field of the Invention
The invention relates generally to electrical apparatus and, more particularly, to insulators for high voltage, high current isolated phase bus disconnect switches.
2. Description of the Prior Art
Disconnect switches for isolated phase bus duct are used to electrically isolate components such as generators, circuit breakers, and step-up transformers. Such a switch is shown in copending application Ser. No. 219,716, filed Dec. 24, 1980 by Alexander Zwillich et al. (now U.S. Pat. No. 4,339,635) and assigned to the assignee of the present invention. This switch employs a conductive outer enclosure at ground potential and an inner conductor coaxially disposed within the enclosure. The enclosure and inner conductor are adapted to be connected to corresponding enclosures and inner conductors of isolated phase bus duct. The inner conductor consists of two fixed components and a telescopically movable contact operable by a mechanism to open and close the circuit. The inner conductor and the movable contact are supported and positioned within the outer enclosure by a plurality of porcelain insulators connected in tension between the enclosure and inner conductor like spokes of a bicycle wheel.
The insulators in the prior art were connected between the enclosure and center conductor by bolting brackets to each end of the insulator, and then welding the brackets to the enclosure and inner conductor, respectively. This created difficulties during assembly of the switch, since the attachment points on the conductors, the enclosure, and the insulators themselves are manufactured to large location and angular tolerances. Thus, extensive fitting and rework was required during assembly in order to provide the required conductor alignment to allow the movable telescoping conductor section to properly mate in both open and closed circuit positions. Assembly using prior art methods of insulator attachment is thus costly and time consuming, requiring a large amount of skilled labor. Furthermore, replacement of an insulator due to damage is awkward in the factory and extremely difficult in the field.
It would therefore be desirable to provide apparatus for attaching insulators between the enclosure and the inner conductor of isophase bus duct and associated disconnect switches which would permit insulator attachment and replacement to be easily made without extensive reworking, both in the shop and in the field.